1. Field of the Invention
The present invention relates to a mobile device, and more particularly to a method and system for increasing the standby battery life of a Global System for Mobile Communication (GSM) mobile device.
2. Description of the Related Art
Since the invention of the first wireless cellular phone, cellular-technology has become the preferred standard for portable wireless communication system across the world. A cellular communications system is usually represented as a honeycombed structure, as indicated in FIG. 1 showing a conventional GSM cellular system. The conventional GSM cellular system includes a plurality of cells 10. Each cell 10 includes a Base Transceiver Station (BTS) 20 equipped with a Radio Transmitter and a Radio Receiver. Each such cell 10 has a range of service over which it caters to a plurality of stationary or roaming mobile units 30. However, a particular mobile unit gets serviced by a unique cell or BTS, as would be evident to anyone skilled at the related art. The same has been indicated in the FIG. 1. It would be apparent to those skilled in the related art that only those aspects of the BTS which are germane to the present invention has been elucidated in FIG. 1, omitting all the other irrelevant intricacies.
An idle-mode process of a mobile unit can be generically described as follows:
1: Looking out for notifications, a.k.a. paging messages, from the Network indicating an incoming call or a short message by reading information out of a Paging Channel (PCH);
2: Gathering the received signal strength, known in the prior art as Received Signal Strength Indication (RSSI), of the serving cell;
3: Scanning the plurality of neighboring cells, surrounding the mobile unit, and gathering the RSSI for each of them; and
4: Evaluating if there is/are any neighbor cell/cells which has/have a higher RSSI compared to the serving cell's RSSI and then making a reselection to a neighboring cell having the greatest RSSI, among the plurality of neighbor cells having higher RSSI than the serving cell, at certain timing. Once reselected, the steps 1 through 4 are repeated in the new cell.
The quality with which the mobile unit is able to meet the first objective of the idle-mode behavior determines the service quality of the cell for that particular mobile unit. A mobile unit is considered to be having good service quality from the serving cell if it is able to decode the network (NW)-transmitted information on the PCH without too many failures.
The battery of a mobile unit is significantly consumed in the process of tuning a Radio Frequency (RF) unit and receiving data from the downlink beacon frequency, and thereby the standby time of the battery is reduced. Accordingly, the average standby time of a mobile unit according to the above four steps 1 through 4 can be expressed as follows:Standby Time(in hours)=[(Battery Capacity in milli-ampere-hours)/(Average Current consumed in milli-ampere)]
From wireless communication protocols, the chief contributing cause to this average current consumption is the operation of the RF unit to monitor, read and/or scan the radio frequencies to achieve the above four idle-mode goals. The operation of an RF unit in the idle mode can be summarized as follows:RF unit activity in idle mode=RF reception on the serving cell's PCH data blocks and gathering RSSI of the same+RF scanning of the neighbor cell's radio frequency to obtain the respective RSSIs.
In light of the above summary, it is apparent that any battery conservation needs to be done by optimizing one or both of the above two factors.
Work done in the prior art has indicated several ways to optimize on the aspect of neighbor cell scanning by reducing the rate at which the neighbor cells are scanned based on certain factors and thereby reducing the use of the RF unit, and hence the current consumption, over a period of time.
A mobile unit monitors its own PCH periodically to look out for any instance of an incoming call. It is network's responsibility to forward the notification of an incoming call to the mobile unit and the network achieves the same by sending the notification of PCH along with the notification of the incoming call, as a paging message, at pre-determined locations in the PCH of which the mobile unit is also aware. A mobile unit knows, in advance, the locations in the PCH where the NW would send the notification for an incoming call. The location or the scheduling of the notification in the PCH is determined in advance and agreed upon between the NW and the mobile unit. The mobile unit evaluates the scheduling period autonomously by making use of certain standard network parameters like BS_PA_MFRMS, a paging period parameter in GSM, and Slot Cycle Index (SCI), in Code Division Multiple Access (CDMA).
Since an incoming call to a mobile unit can arrive practically anytime, the mobile unit reads the data sent in the PCH, at its pre-determined intervals, every time to check if there is an incoming call intended for it. Furthermore, since the wireless communication system does not wish to have poor call performance for a mobile unit, it imposes strict rules on the reception of the paging messages in the PCH. FIG. 2 shows a configuration of multiframes of a conventional GSM downlink. As shown in FIG. 2, a bundle of five multiframes 61, 63, 65, 67 and 69 are periodically repeated. The downlink Broadcast Control Channel (BCCH) carrier (or the beacon frequency) of a GSM cell, which constitutes each multiframe, carries the paging information in the Paging Channels, e.g. PCH 1, PCH 2, PCH 3, . . . , etc. The multiframes become Discontinuous Reception (DRX), where a mobile unit determines the periodic interval when it needs to read the data off the PCH. When a mobile unit does not read the PCH, it shuts down its RF unit and attempts to save battery life. This periodic interval is decided upon by the parameter BS_PA_MFRMS, in GSM, and the mobile units read the PCH data periodically.
FIG. 2 shows a scenario where the NW had used a BS_PA_MFRMS of 5. The mobile units are apprised of the same and they wake up periodically to read the respective paging messages. In the parlance of CDMA, this DRX is replaced with the concept of Slot Cycle Index (SCI). Referring to FIG. 2, it may be known that the mobile unit reads off its own paging message data from the PCH block 2, indicated by PCH2, present on the 0th multi-frame among the bundle of five multiframes periodically repeated. Following that, the mobile unit interrupts the operation of the RF unit 95 for all the PCH blocks occurring in the 1st, 2nd, 3rd and 4th multi-frame 63, 65, 67 and 69. The mobile unit subsequently reads the next instance of paging message from the PCH block 2 once again present on the 5th multi-frame 71, and can identify an incoming call through the paging message. If there is a notification of an incoming call, the mobile unit prepares itself for the call and starts a dedicated connection with the NW. If not, the mobile unit discards the paging message and awaits the next instance of the paging message.
Whenever there is an incoming call for a mobile unit, the NW sends the notification of the incoming call to the mobile unit by paging the mobile unit, using its identity, inside the appropriate PCH block. The mobile unit is expected to listen to all instances of its appropriate periodic paging message and respond to the incoming call. However, it is not guaranteed that the mobile unit will be able to decode a particular paging message, containing the notification of the incoming call, in the very first attempt. The NW, therefore, sends the incoming call notification to the mobile unit once again in the next periodic interval. Typically, the NW sends the notification for that single incoming call to the mobile unit a maximum of K times before giving up. The number of notifications of the incoming call greater than a maximum of K times refers to a maximum number of paging repeats. The value of MAX_PAGE_REPEAT_FACTOR is dependent on the NW and varies from NW to NW.
U.S. Pat. No. 6,628,972 B1, issued Sep. 30, 2003, discloses a method of lengthening the Slot Cycle Index (SCI) of a CDMA based mobile unit in order to read the paging messages in the PCH messages. If the method of U.S. Pat. No. 6,628,972 B1 is mapped to the domain of GSM, it can lengthen the DRX period whereby the mobile unit will skip its assigned PCH read intervals, as indicated by BS_PA_MFRMS, and, instead, read its paging messages alternately or an integral multiple of BS_PA_MFRMS. Skipping the valid PCH reads alternately will reduce battery usage nearly fifty percent. Skipping more will further reduce battery usage. But the scheme proposed by U.S. Pat. No. 6,628,972 B1 has problems including a) an un-deterministic approach which can result in poor Mobile Terminal (MT)-paging performance with frequent paging misses and b) a non-adaptive approach resulting in higher probability of missing MT-paging in a sub-optimal signal condition area, where one may not be able afford missing even one paging message.
The prior art, as exemplified by U.S. Pat. No. 6,628,972 B1, introduces the concept of lengthening the Slot Cycle Index (SCI) or the DRX interval, pertaining to GSM standards, in an arbitrary manner without any deterministic approach. In the prior art, the approach relied on obtaining a time interval from the user of the mobile unit when the user wants to use the mobile phone in a limited manner causes problems. When the time interval starts, the mobile unit increases the SCI or the DRX two times, three times, or ‘N’ number of times, thereby skipping N successive paging messages which it was supposed to have read as per protocol specifications. The user still expects to receive calls, albeit rarely. Whenever there is an incoming call, the NW sends the paging message, indicating the incoming call, a multiple number of times, ranging from 1 to a deterministic number of times, by a MAX_PAGE_REPEAT_FACTOR. If the SCI or the DRX interval is lengthened to a value of ACTUAL_SKIP_FACTOR and if the ACTUAL_SKIP_FACTOR is greater than a MAX_PAGE_REPEAT_FACTOR, the mobile unit will miss an incoming call as it had skipped all those instances of paging messages containing the incoming call notification when the NW actually notified an incoming call. The prior art technique had made no attempt to factor in this aspect into its procedure thereby yielding a battery saving technique with a severe performance-hit loophole.
There is need for a deterministic range for the selection of the value for the ACTUAL_SKIP_FACTOR, and should not be left to a blind selection. Furthermore, the word “rarely” has a very hazy concept in the technical domain. In this case, there can be just two kinds of expectations of a user: (a) the user expects calls or (b) the user does not expect any calls. If (a) the user expects calls, the mobile unit must ensure that it does not miss an incoming call. If (b) the user does not expect any calls, the mobile unit can go into a deep-sleep mode, as would be apparent to those in the related art, and tremendously enhance battery life. As used herein, when the user is expecting calls “rarely,” the user implicitly expects calls and hence, for all practical purposes, falls under the (a) case. Given this expectation, a mobile unit cannot just skip the reading of paging messages in an un-deterministic manner, based on a time interval. Call performance of the mobile unit cannot be compromised.
Additionally, the prior art technique does not suggest any means of determining what the MAX_PAGE_REPEAT_FACTOR can possibly be resulting in a non-deterministic approach. If the mobile unit can get an accurate estimate of the MAX_PAGE_REPEAT_FACTOR, the mobile unit can fine tune its selection of ACTUAL_SKIP_FACTOR value so battery life is saved as long as performance of the mobile unit does not deteriorate. The blind selection of the ACTUAL_SKIP_FACTOR is wrought with severe side-effects, as mentioned in the preceding section. Furthermore, there is no wireless communication system, known in the prior art, which attempts to provide information about the MAX_PAGE_REPEAT_FACTOR to its catered mobile unit. The element of NW-assisted battery saving by transferring the paging repetition factor and the pattern in which the pages would be transmitted is missing in the prior art.
There is yet another important aspect missing in the prior art technique of lengthening the DRX interval or the SCI interval, which makes the approach susceptible to low signal conditions or varying signal conditions thereby resulting in sub-optimal MT-call performance. Presume, for example, that the prior art decides to use an ACTUAL_SKIP_FACTOR of 1. This means that the mobile unit now reads its own valid paging messages alternately. Presume also that the mobile unit is roaming in an area where signal conditions are not good. The mobile unit reads the first paging message and finds out that there is no incoming call for itself. The mobile unit also gets an estimate of the air interface, RSSI and Signal to Noise Ratio (SNR), and found that it is not good. As per techniques in the prior art, the mobile unit blindly skips the next paging message to facilitate the battery saving process. Presume that there was an incoming call at this instant and the NW had sent the notification to the mobile unit on that paging message. The mobile unit could have decoded the paging message at this instant, but it had skipped. The NW would send the notification once again in the subsequent paging message. But as the signal conditions are not good, the mobile unit fails to decode the paging message in this attempt and subsequent ones also. This leads to a miss of an MT call. The prior art techniques, employing blind paging skips, thereby fail to account for deteriorating signal conditions. Such a scenario is not unlikely in the life of a mobile unit, especially when the mobile unit is wandering through a high-interference region.
As described above, no attempt has been made in the prior art technique to intelligently handle a battery-saving procedure when signal conditions became bad or are in a process of deterioration. In such signal conditions, a mobile unit cannot afford to miss a single paging message as it has no guarantee about its success in decoding the subsequent paging messages.